Add pi3b hardware tier and resource guards for condo Pi deployment

- Add pi3b tier (700MB RAM limit, 8 passive/2 active modules, no bettercap/mitmproxy)
- Update detect_hardware_tier() to detect Raspberry Pi 3B by model string and BCM2837
- Add pi3b section to hardware_tiers.yaml
- Add systemd MemoryMax/CPUQuota/OOMScoreAdj to all three service files
- Fix bigbrother-watchdog.service ExecStart (was calling non-existent ResourceMonitor().run())
- Add scripts/run_watchdog.py as standalone health monitor daemon

services/bigbrother-capture.service

@@ -12,6 +12,9 @@ RestartSec=5
 User=root
 StandardOutput=null
 StandardError=null
+MemoryMax=80M
+CPUQuota=50%
+OOMScoreAdj=300
 
 [Install]
 WantedBy=multi-user.target